There have been many proposals for, and attempts at, utilizing insects to process waste materials, especially animal manures, into valuable products. For the most part, these schemes have not worked well, or the level of productivity has not been great enough to support the process, typically due to operating and labor costs. Most often, these are batch processes that have included loading a culture vessel with a large quantity of larval feed (manure or other wastes), adding an appropriate number of insect eggs or first-stage larvae, allowing time for the larvae to consume the feed, followed by harvest of the mature larvae or pupae. Unfortunately, such systems provide less than optimum nutrition for the larvae because, during the days or weeks that the larvae are in the culture, the feed is also undergoing microbial decomposition and spoilage, thus reducing the conversion efficiency of the larvae. If this problem is avoided by daily feeding, the labor requirement severely limits the scope of an operation.
Continuous culture systems have also been proposed, especially for flies that have migrating larvae, for example the black soldier fly, whose larvae leave the feeding location before pupation. Such systems have been proposed for use under animals housed on slatted floors or in wire cages, and for small systems used to treat small-scale food processing waste streams and restaurant waste. In all these cases, the larvae are usually fed at least once per day, overcoming the limitations of adding several weeks of larval feed at the same time that small larvae are added. However, there is often difficulty in matching larvae numbers and larval feed supply and achieving optimum self-harvest. If the population is in significant excess of the larval feed supply, immature larvae may leave the culture tray or basin, thus missing their most rapid growth and greatest larval feed consumption period. If the larval population is significantly below the larval feed supply, some areas of the culture tray will be unoccupied by feeding larvae, thus providing a location for migrating larvae to undergo pupation without actually leaving the culture tray or basin and leading to production of at least some flying adults.
From the foregoing discussion it can be appreciated that it would be desirable to have an improved system and method for rearing larvae that overcomes one or more of the disadvantages described above.